Force balancing device for a hoist with two traction cables and hoist fitted with such device

ABSTRACT

The invention concerns a load balancing device consisting of a planetary or trochoidal mechanical differential speed reducer, arranged on a winch comprising two drums and enabling to balance the torque exerted on the drums. Thus, if a cable is improperly wound on one of th drums, the balancing device enables the tensile load exerted on each wire to remain identical. Such a device is particularly efficient to ensure security for a working platform operating on a building facade.

BACKGROUND OF THE INVENTION

The present invention concerns a balancing device for traction forces,specifically intended for a hoist, that is supposed to simultaneouslywind or unwind two or more traction cables, as well as a hoist fittedwith such a device and a gondola equipped with at least one hoist ashereinabove.

Such hoists, particularly those comprising a twin winding organ,traction drums or traction sheaves where each of said organs carries itsown cable, find numerous applications. Particularly in certainconfigurations they are employed for lifts or more specifically forgondolas engaged in the cleaning and/or upkeep of the facades ofhigh-rise buildings. Such a gondola usually is held by four cables, afirst pair of cables being arranged at a first short side of the gondolaand the second pair of cables being arranged at the second short side ofthe gondola. Each pair of cables is wound/unwound from a hoist equippedwith two drums, with each hoist having its own motor that is controlledindependently of the other motor. Thus, the speed of winding/unwindingof each hoist is so adjusted by known mechanical, electric, orelectronic means that each pair of cables is unwound or wound with thesame speed and the gondola will remain horizontal. For the two cables ofa given pair, to the contrary, since their winding or unwinding speed iscontrolled by a single hoist or by just one motor, said means cannot beemployed to preserve their balance. An unbalance between the two cablesof a pair may arise, for instance, when the winding of one of the cableson its drum is irregular and causes subsequent windings to be wound witha larger diameter than that of the windings of the other cable. In thiscase the cable being wound up on a larger diameter will tend to assumethe full traction force, which may lead to

an unbalance of the gondola or, by rupture of this overly loaded cable,to risk for the workers riding this gondola.

A first mechanical means that allows an identical tensile stress to bepreserved for the two cables of a given pair, even in a situation whereone of the cables is poorly wound, consists of bringing the two cablestogether on one sheave. Such a device may be dangerous in the instanceof rupture of one of the cables, since the other cable then becomesfree, and the gondola is no longer held by either of the two cables.

According to other means, the two cables are attached to the two ends ofa spreader while the center of this spreader is hinged to the suspensionbeam or to the gondola. This device will not encounter the drawbackmentioned earlier, but now the difference in lengths that can beadmitted between the two cables is limited by the length of thespreader.

In the two means described above, the balancing device—sheave spider orcenter of the spreader—is attached to the gondola or suspension beam ina single point, which in the final analysis is detrimental to thegondola's balance. FR-A-2 183 594 describes a device with differentialfor a crane lifting hoist. Using this device the operator controlssequentially rather than simultaneously a lifting operation and a masttelescoping operation. There is no indication anywhere in this documentthat the device permits a simultaneous actuation of both drums.

WO 88/05999 describes a differential device allowing the forces on twotraction cables of a trawl to be balanced. This document explicitlydescribes that the operations of launching of the trawl as well as thoseof hauling it in do not involve the use of the differential device,which is put in operation, only during the fishing, that is, when thehoists are inactive.

SUMMARY OF THE INVENTION

The invention provides a force balancing device for a hoist intended forat least one pair of traction cables that will allow the drawbacksmentioned earlier to be avoided.

It is an objective of the invention to propose a hoist that is intendedfor at least one pair of traction cables and is fitted with at least oneforce balancing device that is capable of ensuring at all times thesafety of the object suspended on the cables.

It is yet another objective of the invention to propose a gondola forfacade upkeep that is fitted with at least one hoist equipped with aforce balancing device.

These objectives are attained by a balancing device, a hoist, and agondola having the characteristics mentioned in the independent claims,while specific embodiments or variants are described in the dependentclaims.

The below description describes several embodiments of a deviceaccording to the invention, and should be read in conjunction with theattached drawing comprising the figures where

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation of part of an installation for facade cleaning,

FIG. 2 is an end view of part of the installation of the precedingfigure,

FIG. 3 is a view in longitudinal section of a first embodiment of abalancing device according to the invention,

FIG. 4 is a partly sectioned front view of the device of the precedingfigure,

FIG. 5 is a view in longitudinal section of a second embodiment of abalancing device according to the invention,

FIG. 6 is a partly sectioned front view of the device of the precedingfigure, and

FIG. 7 is a schematic representation of the operation of part of thedevice of FIGS. 5 and 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 and 2, one has a building 1 with a vertical facade 10 and aroof 11, here represented as being a flat roof. Building 1 is equippedwith an installation 2 for cleaning/upkeep of the facade 10 comprising agondola 20 suspended from a first pair of cables 21 and a second pair ofcables 22, with two support beams 23 and 24 fixed on a frame 25 thatpreferably can move on the roof 11 so that the gondola 20 will be ableto reach all of the facade 10.

The gondola 20 that is shown here comprises more particularly two endfaces 20A and 20B each carrying a hoist 3 allowing the gondola 20 to beraised or lowered along the facade 10. The first hoist 3 comprises moreparticularly a first motor 30, preferably an electric motor, a firstreduction gear 31, as well as two drums 32 and 33 mounted coaxially atthe wall 20A, while the second hoist comprises a second motor 34, asecond reduction gear 35, and two further drums 36 and 37 mountedcoaxially at the wall 20B. The two drums 32 and 33 of the first hoisteach take one cable 210 or 211, respectively, of the first pair ofcables 21 while the two drums 36 and 37 each take one cable 220 or 221,respectively, of the second pair of cables 22. The free ends of cables210 and 211 of the first pair 21 are attached to the beam 23, preferablydetachably, while the free ends of cables 220 and 221 are attached inlike manner to the beam 24.

A control unit 38 supplies and controls each of the motors 30 and 34.

Optionally and depending on the configuration that is selected for thedrums, the gondola may also comprise two additional units shownschematically at 39 which are suitable for performing one of more of thefollowing functions: changeover of the cables 210, 211 and 220, 221distributed along an axis parallel to the axis of rotation of the drums,as shown in FIG. 1 in the space between the drums and the units 39, to aconfiguration where each cable pair is arranged within a planeperpendicular to the above mentioned axis, as shown in FIG. 2, or, inanother embodiment of the gondola that is not represented in thefigures, to a plane parallel to said axis, in the section situatedbetween the unit 39 and the beam 24, level winding of each cable on itsdrum, and safety brake blocking the cable or cables when a cable ruptureis detected. These different means are known in the art and will hencenot be described in more detail here.

An irregular winding of one or several of the above cables on one orseveral of the drums mentioned may lead to an unbalance in the loaddistribution between the cables 210 and 211 or 220 and 221, or to anunbalance of the gondola 20 that corresponds to an angular slippageabout the longitudinal axis of roll R or an angular slippage about thetransverse axis of pitch T, or to a combination of these two slippages.

In the embodiment represented, slippage about the axis T when presentcan be compensated by acting on the relative speeds of the two motors 30and 34, either by an organ for automatic detection of said slippage ormanually via the control unit 38.

Since the two drums 32 and 33 of the first hoist or the two drums 36 and37 of the second hoist are controlled by a single motor 30 or 34,respectively, it is not possible to compensate slippage about the axis Rby the means just mentioned.

It is proposed to this effect according to the invention to instal amechanical balancing device between the two drums, 32 and 33 or 36 and37, respectively, of each hoist.

According to a first embodiment, the balancing device consists of amechanical differential reduction gear with three axles, as for instancethe planetary gears 4 as shown in FIGS. 3 and 4. The device 4 comprisesan input shaft 40 that is driven directly by the motor 30 or 34 or bythe reduction gear 31 or 35, as needed. A sun gear 41 is solidly mountedon the shaft 40. One or several planet gears 42 engage, on one hand withthe sun gear 41 and on the other hand with an external race 43 withinternal teeth. The race 43 carries the drum 32 or 36 that is part of alifting mechanism. Each of the planet gears 42 is pivoted on an axle420, while said axles are fastened to a flange 44 that freely pivotsabout the end of shaft 40. Flange 44 carries the drum 33 or 37.

Looking at FIG. 4 and assuming that the shaft 40 or sun gear 41 turnsclockwise, while blocking the drum 32 or 36 or the race 43,respectively, one can see that the flange 44 that carries the drum 33 or37 also turns clockwise. If to the contrary one blocks the drum 33 or 37or the flange 44, respectively, one can see that the drum 32 or 36 turnscounterclockwise while the shaft 40 turns clockwise. Thus, in order toobtain a simultaneous ascending or descending motion of the gondolaaccording to the direction of rotation of the shaft, it will benecessary that the two cables of one pair be wound up in oppositedirections onto the two drums, as seen in FIG. 4.

The balancing device 4 for the traction forces functions as follows, inthe situation where the two cables of one pair exert the same tractionforce on the two drums or identical torques are exerted, respectively,the two drums are rotated in opposite directions when the shaft 40 isrotated, and thus cause the gondola to ascend or descend, depending onthe direction of rotation of shaft 40. In a situation where one of thecables is wound up with a diameter that is different from that of theother cable, which causes the force exerted on one of the cables to bemore important than that exerted on the other cable, then the drumholding the more highly taut cable will block and cause the motionperformed by the other drum to continue until the difference in forcesis made up and the forces exerted on the two cables are once moreessentially identical.

One thus has a differential balancing device between the two drums whichacts so that, when one cable is more highly taut than the other, thetorque created on the drum by this taut cable causes the race or flangeadjacent to this drum to become a fixed point of the device, thusallowing the other element, flange or race, as well as the adjacent drumto make up this difference in tension, no matter whether the drive shaftis driven or not. Through this device the two cables of a pair of cablesare thus always subject to essentially identical traction forces, evenif the speeds of rotation of the two drums are not identical.

Design versions of this device that differ from the one just describedcan be envisaged. For instance, the size ratios of the different gearwheels that are present may be different from what has been described orrepresented, just like known design variations of triaxial planetreduction gears, for instance, a number of planetary gears that isdifferent from the number shown here, or another way of meshing of thegear wheels.

A second embodiment of a balancing device according to the invention isrepresented in FIGS. 5 and 6. This device, which is again a mechanicaldifferential reduction gear with three axles, essentially corresponds toa trochoidal (cycloidal) reduction gear such as that known by the nameof “Cyclo” (registered trade mark), a specific embodiment of which isdescribed in EP 0 291 052.

This device 5 comprises an input shaft 50 that, like the shaft 40 of thepreceding device, comes directly from the drive motor or from anintermediate reduction gear. The shaft 50 comprises an eccentriccyclindrical bearing surface 51 that is fixed on the shaft. Theeccentric bearing surface causes eccentric rotation of a toothed wheel52 that has a central cylindrical bore 520, or equivalent means forrotation mounted on the eccentric bearing surface 51, external teeth 521of which a specific embodiment will be described in greater detailbelow, as well as a plurality of circular bores 522 regularly spacedalong a diameter that is coaxial to the central bore 520 and to theteeth 521. The device 5 additionally comprises an external race 53 withinternal teeth 530 of which a specific embodiment will also be describedbelow, and which in part engages with the teeth 521 of the wheel 52. Aflange 54 is freely pivoted on the shaft 50 and supports a plurality ofprotruding rods 540, each of them corresponding to a bore 522 of thewheel 52. It can be seen in the figure that the bores 522 have a largerdiameter than the rods 540; this device of bores and rods actuallyserves to transpose the eccentric rotary motion of the wheel 52 to aconcentric rotary motion of the flange 54 about the shaft 50. To thiseffect the diameter of a bore 522 is equal to the diameter of a rod 540plus the amount of eccentricity of the wheel 52. One may have one ormore sets of bores and rods for the transmission of this motion, and itis also feasible that one or several bores are arranged on the flange 54while the corresponding rod or rods are attached to the wheel 52. Theexternal race carries the drum 32 or 36 which holds the cable 210 or220, respectively, while the flange 54 carries the drum 33 or 37 whichholds the cable 211 or 221, respectively.

FIG. 7 shows a preferred embodiment of part of the device justdescribed, showing the engagement of wheel 52 in the race 53. The race53 has a plurality of semicylindrical bearings 531 each holding a roller532 freely turning in said bearing 531. In the example represented, therace 53 comprises twenty bearings 531 and as many rollers 532. Theeccentric wheel 32 has a plurality of semicylindrical bearings 523 onits periphery, the number of said cylindrical bearings here being oneless than that of the rollers 532. One will thus understand that, whenthe race 53 is blocked, one has one revolution of the eccentric wheel 52for any nineteen revolutions of the shaft 50, or one revolution of theflange 54 or of the drum 33 or 37 supported by this flange, for onerevolution of the shaft 50. When blocking the flange 54 or the drum 33or 37, or the wheel 52, respectively, to the contrary, one has twentyrevolutions of the race 53 or of the drum 32 or 36 supported by thisrace, respectively, for one revolution of the shaft 50.

It is an advantage of a differential trochoidal balancing deviceaccording to this second embodiment described, over the planetary deviceaccording to the first embodiment described, that the ratio of speeds ofthe drums to the speed of the drive shaft is distinctly larger, so thatit becomes possible with a trochoidal balancing device according to thissecond embodiment to omit placing a speed reduction gear 31 or 35between the motor and the input shaft 50 of the balancing device.

Different design variants of a differential trochoidal balancing devicecan be envisaged; for instance, one can have a difference between thenumber of rollers 532 and the number of bearings 523 on the wheel 52that is larger than one, for instance two or three. Likewise, theexternal teeth 521 of the wheel 52 and the internal teeth 530 of therace 53 may differ from those described here, that is, one may haveconventional teeth 521 and 530 where one or several teeth are engagedsimultaneously. The differential trochoidal balancing device may also bedesigned like that described in the document EP 0,291,052, that is,comprising several wheels 52 in parallel, and eccentrically offset so asto distribute the forces in a softer and more regular way.

Other types of reduction gear can also be provided to function as abalancing device. For instance, a reduction gear of the registered trademark Harmonic Drive, or more generally a differential mechanicalreduction gear of the kind found in a car could very well perform thedesired function of balancing the traction forces. Generally, anydifferential mechanical reduction gear mounted between the two drumscould be used as a balancing means. Preferably, so as to have a compactdevice, a triaxial reduction gear will be used.

A balancing device according to one or the other of the embodimentsenvisaged can be made more complete by adding a disconnecting means, forinstance a latch which will allow facile unwinding of the cables fromtheir drums when the gondola is at ground, on order to attach them tothe suspension beams.

A balancing device according to one or the other of the embodimentsenvisaged can also be employed in a hoist fitted with two tractionsheaves, rather than two drums; preferably, the traction sheaves willthen be fitted with known means helping to make the cable adhere to asegment of the sheave's periphery.

The gondola described above, and shown in the figures, is conceived withthe four cables, each fastened at one corner of the gondola, but otherconfigurations for attachment of the cables can also be envisaged, forinstance with the four cables aligned in a plane holding thelongitudinal axis of the gondola.

Also, the gondola has been described with the hoists 3 mounted on board;but one could just as well have an installation where the two hoists 3are arranged outside of the gondola, for instance on the structure 25supporting the beams 23 and 24 or directly on these beams. In thisembodiment one could even have a single hoist driven by just one motor,with the axle of the motor holding two sets of drums and each set ofdrums comprising a balancing device according to one or other of theembodiments described. Thus, a single hoist or a single motor shaft mayvery generally comprise several pairs of drums and/or traction wheels,each pair with its own balancing device.

The balancing device according to one or other of the embodimentsdescribed, like the hoist having such a balancing device, have beendescribed and represented as employed with a gondola for the upkeep of afacade of a building; but both the balancing device and the hoist can beemployed in many other applications.

What is claimed is:
 1. A balancing device for traction forces exerted bytwo cables on two means of winding simultaneously rotated by motorizedmeans, comprising a differential mechanical reduction gear with adriving axle and two driven axles, said motorized means driving thedriving axle and said two means of winding being connected with the twodriven axles, said two means of winding turn in opposite directions toproduce a common winding or unwinding motion of the two cables.
 2. Abalancing device as set forth in claim 1, wherein the differentialmechanical reduction gear is a planetary reduction gear.
 3. A balancingdevice as set forth in claim 1, wherein the differential mechanicalreduction gear is a trochoidal reduction gear.
 4. A balancing device asset forth in claim 2, including an input shaft bearing a sun gear, atleast one planet gear attached to and rotating with a flange freelyturning about an axle coaxial to said input shaft, an external race withinternal teeth, said planet gear(s) engaging on one hand with the sungear and on the other hand with the external race, the flange supportingone means of winding and the external race supporting the other means ofwinding.
 5. A balancing device as set forth in claim 3, comprising aninput shaft fitted with at least one eccentric cylindrical bearingsurface, at least one toothed wheel comprising external teeth freelyturning on said eccentric cylindrical bearing surface, as well as atleast one means for transposing an eccentric circular force to aconcentric circular force, an external race with internal teeth engagingwith the teeth of said toothed wheel, a flange freely turning about anaxle coaxial to said input shaft and rotated by said means oftransposition of an eccentric circular force to a concentric circularforce, the flange supporting one means of winding and the external racesupporting the other means of winding.
 6. A balancing device as setforth in claim 5, wherein the internal teeth of the external raceconsist of a first number of first semi-cylindrical bearings, eachholding a roller freely turning in said first bearing, the externalteeth of the wheel consisting of a second number of second cylindricalbearings engaging with the parts of the rollers not contained in saidfirst bearings.
 7. A balancing device as set forth in claim 6, whereinthe first number of first bearings is higher than the second number ofsecond bearings.
 8. A balancing device as set forth in claim 7, whereinthe difference between the first number of first bearings and the secondnumber of second bearings is at least one.
 9. A balancing device as setforth in claim 5, wherein said means of transposition of an eccentriccircular force to a concentric circular force comprises at least one rodparallel to the input shaft and cooperating with a circular bore theinternal diameter of which is equal to or greater than the externaldiameter of the rod plus the eccentricity of said eccentric cylindricalbearing surface.
 10. A balancing device as set forth in claim 9, whereinat least one of said circular bores is arranged on the toothed wheelwhile at least one of said rods is fastened to said flange.
 11. Abalancing device as set forth in claim 9, wherein at least one of saidcircular bores is arranged on one of said flange and toothed wheelmembers while at least one of said rods is fastened to the other of saidflange and toothed wheel members.
 12. A balancing device as set forth inclaim 1, wherein it is made more complete by adding a reduction gearacting on the input shaft.
 13. A balancing device as set forth in claim1, including a guide mechanism fit to cause the cables to change from afirst arrangement where said cables are spaced along an axis parallel tothe axis of rotation of the means of winding to a second position inwhich said cables are arranged in a plane perpendicular to said axis,and vice versa.
 14. A balancing device as set forth in claim 1,including a level wind guide fit to distribute each cable side by sideon its respective means of winding while said cable is wound up on saidtwo means of winding.
 15. A balancing device as set forth in claim 1,including an emergency brake mechanism fit when said mechanism detects arupture in one cable to block the other cable.
 16. A balancing device asset forth in claim 1, arranged as a hoist for the simultaneous windingor unwinding of said pair of cables.
 17. A hoist as set forth in claim16, wherein said two means of winding comprises two drums.
 18. A hoistas set forth in claim 16, wherein said two means of winding comprisestwo traction sheaves.
 19. A hoist according to claim 16, including agondola for the upkeep of a facade.